Abstract
Simple SummaryThe olfactory sensillum, which is located in the antenna of insects, is the basic unit of the olfactory organ. Olfactory-related genes are expressed in the sensillum. It is believed that the process of olfaction recognition is mainly mediated by two gene families, odorant binding proteins (OBPs) and olfactory receptors (ORs). The honeybee possesses a large numbers of ORs, but few OBPs. Up to now, the function of OBPs in the honeybee has not yet been fully elucidated. In order to reveal the specific role of OBPs from Apis cerana cerana, we selected an OBP gene, AcerOBP6, which is highly expressed in the antennae of worker bees, acquired a purified protein via a prokaryotic expression system, and analyzed its function using bioinformatics, molecular biology, and electrophysiology. According to the result, AcerOBP6 was a protein with extensive binding affinity, and we speculated that its function was chiefly related to foraging. Overall, this research not only explains the essential role of OBPs in ligand binding, but also provides valuable resources to help researchers further understand the nature and mechanism of the olfactory system.Olfaction is essential in some behaviors of honeybee, such as nursing, foraging, attracting a mate, social communication, and kin recognition. OBPs (odorant binding proteins) play a key role in the first step of olfactory perception. Here, we focused on a classic OBP with a PBP-GOBP domain from the Asian honeybee, Apis cerana cerana. Beyond that, the mRNA expression profiles and the binding affinity of AcerOBP6 were researched. According to qRT-PCR analysis, AcerOBP6 transcripts were mainly expressed in the antennae of forager bees. In addition, we found that the expression level of AcerOBP6 was higher than that of AmelOBP6. The fluorescence competitive binding assay indicated that the AcerOBP6 protein had binding affinity with most of the tested odors, including queen pheromone, worker pheromone, and floral volatiles, among which the strongest one was linolenic acid (with a Ki value of 1.67). However, AcerOBP6 was not sensitive to the brood pheromones. A further study based on EAG assay revealed that the antennae had the strongest response to 2-heptanone. The EAG recording values of the selected ligands were all reduced after AcerOBP6 was silenced, with 8 of 14 declining significantly (p < 0.01) given that these odors could specifically bind to AcerOBP6. As revealed in our current study, AcerOBP6 might be a crucial protein involved in olfactory recognition for foraging. Overall, the research provides a foundation for exploring the olfactory mechanism of A. cerana cerana.
Highlights
Licensee MDPI, Basel, Switzerland.Olfaction plays a significant role in the survival and reproduction of insects by modulating several of their biological behaviors
The results of homology analysis for homologous proteins showed that AcerOBP6 had a high identity with its sibling species (Figure 1), such as 90% to AmelOBP6 and 88%
Results, the AcerOBP6 transcript was primarily expressed in the antennae of forager bees and significantly more expressed than in the antennae of drones, suggesting that AcerOBP6 may play an essential role in recognizing general odorants compared to sex pheromones
Summary
Olfaction plays a significant role in the survival and reproduction of insects by modulating several of their biological behaviors. The antennae are the main olfactory organs, with a large number of olfactory sensilla located on them [1,2,3]. OBPs, as the soluble carrier proteins with a small molecular weight (~130–150 amino acids), are secreted in the sensillum lymph of the antenna [4], and function as the first filters for odor recognition and interaction. Deliver them to ORs (olfactory receptors) to trigger olfactory behavior [4,5]. The OBPs of insects and vertebrates are exceptionally stable to thermal and solvent denaturation [6], which makes it possible to obtain reliable proteins whose physiological functions can be researched in vitro
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